The administration of many medications requires specific dosing regimens that occur over a relatively long period of time. To this end, the development of syringe pumps has dramatically benefited patients needing volumetrically proportioned delivery of their medication. Syringe pumps generally comprise a barrel, or syringe, and mount to a housing. The syringe is typically filled with one or more chemical, nutritional or biological substances that are mixed into a uniform solution. A pusher associated with the pump forces a plunger through the syringe. As the plunger travels through the syringe, the medication is forced out into flexible tubing and/or catheters and into the patient.
During the course of delivering the medication to the patient, it is possible for an occlusion to arise in the delivery path. Examples of occlusions may include a closed stopcock, slider valve or pinched line. Such a condition, if undetected, may cause injury to the patient. That is, when an occlusion occurs along the delivery path, medication is not delivered to the patient even though the pump continues to function. Thus, an occlusion prevents the infusion pump from delivering medication to the patient until the occlusion can be detected and cleared from the infusion path. For this reason, the rapid detection of occlusions along the delivery path is key to reliable pump operation.
An occlusion in the infusion line will cause the force, or pressure, in the syringe to increase. In turn, force between the pusher of the syringe pump and the syringe plunger will increase. Conventional pumping systems use a transducer to monitor force between the pusher of the syringe pump and the syringe plunger, or the pressure in the syringe. Other more costly pumping systems position a disposable sensor within the actual delivery line.
In such prior art pumps, an alarm is generated when the force between the pusher and the plunger or the pressure in the syringe increases above a predetermined threshold. As such, the alarm is either “on” or “off” depending on whether the threshold has been met. As a consequence, the user has no way to know whether the pressure in the syringe is building up to an unacceptable level that precedes the threshold. The user only knows when the alarm is reached. Thus, remedial action can only be taken once an infusion protocol has already been potentially compromised.
This circumstance is compounded where the threshold is set to a relatively high value to avoid false occlusion alarms. At low delivery rates, a conventional pump may take hours to reach high enough line pressure to trigger conventional alarm systems. This detection period delay would ideally be around five minutes or less to avoid having a negative impact on patient care.
Still another obstacle to occlusion detection arises in the context of bolus injections, where a relatively large volume of medication is delivered in a relatively short period of time. In such bolus applications, the pressure in the pump will easily exceed the threshold alarm level, irrespective of the presence or absence of an actual occlusion. Similarly, widely varying pressures that occur during the initial, ramping stage of a non-bolus delivery render conventional detection methods unreliable in the face of varying flow rates. Thus, it is extremely difficult to detect whether the deliver line is occluded during stages of both bolus and non-bolus pumping applications.
As a consequence, there exists a need for an improved manner of automatically detecting an occlusion within a fluid line with a medical infusion system.